Si/Si/sub 1-x/Ge/sub x/ heterojunction bipolar transistors fabricated by limited reaction processing

The DC performance of Si/Si/sub 1-x/Ge heterojunction bipolar transistors (HBTs) fabricated from epitaxial layers grown by limited reaction processing is presented. The highest gain ( approximately=400) device has a 20-nm, 31%-Ge base heavily doped with boron to a level of 7*10/sup 18/ cm/sup -3/. Measurements of the collector current as a function of temperature yield values of the valence band discontinuity, Delta E/sub v/, for four different Ge compositions. The dependence of Delta E/sub v/ on Si/sub 1-x/Ge/sub x/ layer thickness was also measured and found to decrease as strain relaxation occurred.<
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